Detection of Conduction Electron Spin Polarization in n-GaAs by Negative Muonium

In our ZF μ+ SR studies of the spin-dependent response to the polarized conduction electrons produced by circularly polarized 830 nm laser light in a semi-metallic and strain-free n-type GaAs (3×1016 cm-3 Si), among possible states of positive muon, Mu− (μ+e−e−) had been found to take a spin-dependent exchange scattering, while muonium (Mu0) at bond-center was found to be insensitive. In order to understand this surprising spin-dependent Mu− response, the LF (up to 0.4 T) μ+SR studies were carried out and data is suggesting a contribution of bound electron(s) of Mu−. Possible mechanisms of the Mu− response are given.